How I shot this

Published on 17 March 2018

Well, what is it?

This is the Sun, our closest star and the source of all life on Earth, as it looked on Monday 5 March 2018.

The Sun is a massive fiery ball of energy without which our planet would simply be a frigid lifeless rock. It is by far the largest object in the solar system and holds more than 99,8% of its mass. The solar disk is approximately 1,3 million kilometers across or 109 times the Earth's diameter, meaning that Earth is about the size of an average sunspot. The Sun weighs approximately 1.989 x 10^30 kg - or 1,989,000,000,000,000,000,000,000,000,000 kg. That doesn't really mean much. It's about 333,000 times more than Earth, an equally difficult-to-grasp number.

The Sun's visible surface, the photosphere, is around 5,500 degrees Celsius and its core is estimated to be some 15,000,000 degrees Celsius. Every second the Sun loses about 4 million tonnes of mass due to the nuclear fusion at its core and another 1,5 million tonnes due to the solar wind. This means that the Sun's mass decreases over time and has done so for the 4,5 billion years that the Sun has been around. Still, so far it has only burnt an estimated 0,05% of its mass, or the equivalent of around 100 times the mass of Earth. 

But, due to this ongoing mass loss scientists expect that the Sun will have consumed most of the hydrogen which fuels its internal fusion in some 5 billion years at which point it will swell up to a red giant, probably out to Earth's orbit. At some later point the star will shed its outer layers which will turn into some form of, naturally very beautiful, nebula at the centre of which will be the last remaining core of the Sun, an approximately Earth-sized white dwarf star consisting mostly of carbon and oxygen.

As impressive as all these numbers are, the Sun is actually just average as stars go. On the Morgan-Keenan system of stellar classification - which runs from O, B, A, F, G, K, M (the handy mental clue is Oh, Be A Fine Girl Kiss Me) - the Sun is just a G class yellow dwarf star. But she's a beauty, nonetheless. In fact, there are two things in partcular that stand out about the Sun. One is that she is alone; most stars tend to have one or several companion stars. The second thing is naturally that as far as we know it's the only star with an orbiting planet home to life.

: : Warning : :

Solar photography must never be undertaken without appropriate filtration. There is otherwise an extremely serious risk of permanent damage to one's eyes, including blindness, not to mention the likely total frying of one's observing and photographic equipment. And, of course, be careful when looking at the Sun. It helps to use solar viewing glasses or at least sunglasses when trying to line up the camera or find the Sun in a viewfinder.

Filters

Filtration can be done with simple add-on filters, attached to the front of the camera's lens or of the telescope, or more complicated filters for telescopes which attach both at the front of the lens and at the eyepiece. 

The front-mounted filters come in several varieties, from glass filters which show the Sun as yellow, to Mylar filters which give a blueish tint to the image, to specialised filters which show the Sun as white, which I feel is more correct; it is Earth's atmosphere which filters the sunlight to make the Sun look yellow. With such filters one can see sunspots, for instance. There are several brands manufacturing these filters, for instance Baader Planetarium GmbH and Thousand Oaks Optical.

The more complicated, and considerably more expensive, filters display only a very narrow part of the spectrum called helium-alpha or H-Alpha for short. With these filters one will see the layer outside the photosphere, called the chromosphere, where a lot of very dramatic action happens, such as the specacular prominences which can rise 150,000km.

There are supposedly also other ways to observe or photograph the Sun, including through stacked ND filters and welding masks, but I cannot comment on their safety or usefulness.

For this photo I used a filter I made myself from a sheet of the Baader Planetarium Astro Solar Safety Film, which I attached with superglue to the lid of a pipe tobacco tin. Believe it or not, but that lid fit almost perfectly to the front of the Tele-Tessar. The duct tape around the hole I cut in the lid was to prevent the sharp edge to destroying the film (and had the useful side-effect of making the filter look even more horribly home-made). 

The Astro Solar Safety film has an optical density of 5,0 and provides 100% UV and IR protection and reduces the intensity of the Sun's visible light by 99,999%. As a consequence the solar disk appears quite dark in the viewfinder, certainly not very luminous at all, with a knock-on effect on the shutter speeds. Baader also sells a film with optical density 3,8 which renders the solar disk brighter to allow for faster shutter speeds. I elected not to buy that filter because of the warning on Baader's website that it is not suitable for "visual solar observation", which is what I would be doing by pointing, in essence, a very large magnifier at a star. That filter might work with indirect solar photography using the live view on a DSLR, for instance.

Camera and lens considerations

If one decides to go the digital or film camera route for solar photography there's first the question of format to be addressed. There are of course many formats, from several crop formats such as APS-C, to "full frame" digital cameras and their equivalent 35mm (24x36mm) film siblings, to larger formats, like medium and large format. It is also possible to photograph the Sun with the help of telescopes or spotting scopes using attached dedicated digital cameras or with ordinary digital or film cameras attached to the scope's eyepiece in various ways. Since I don't have a telescope or spotting scope I will in the following focus on cameras only.  

Anyone who has ever tried to shoot the Moon will know that it is painfully small in the frame even with medium-length telephoto lenses. Since the Sun appears to be of relatively similar size as the Moon from our vantage point here on Earth, the same applies to it. On a 24x36mm frame one really has to use quite long focal lengths for the Sun to be anything but a smaller dot. With a focal length of less than around 400-600mm the Sun will be too small for an interesting photograph. Here are examples from Canon from both full frame and APC-C cameras. 

With respect to the roughly 55x55mm frame of a square medium format negative or transparency one needs to go even longer to obtain an suitable size of the solar disk. It is always tricky to compare a square format to a rectangular one, but in the context of solar photography I prefer to use the vertical angle of view since the Sun is round. A 350mm lens for my Hasselblad will have an equivalent vertical angle of view in 35mm of only 149mm (see here for comparisons). One 'loses' a lot of focal length by using a larger film format. Naturally similar considerations apply if one uses larger-sensor digital medium format cameras. I mentioned large format earlier but such cameras are not particularly useful for solar photography. In fact, smaller-than-full-frame digital cameras may be the easiest way to obtain a larger solar disk in the frame.

But all the above considerations notwithstanding I chose to use my Hasselblad 203FE and a Carl Zeiss 350mm Tele-Tessar f/4. To get a longer focal length I stacked not one, not two but three extenders: a 2x Carl Zeiss Mutar, a 2XE Hasselblad extender and a 1.4x PC-Mutar, a shift converter which I used in neutral position. This gave me an effective focal length of 1960mm, meaning an equivalent vertical angle of view of a 35mm camera of around 830mm. Not very long, in other words.

Tripod

A tripod is required for this type of photography because the solar disk is not particularly bright through the Baader Astro Solar Safety Film. In fact, I used two tripods, a comparably sturdy Manfrotto 055 attached to the tripod collar on the 350mm Tele-Tessar and another, smaller tripod attached to the camera. From past experience, I knew that there would be too much movement with only the large tripod, even if I shot with the mirror locked up and a 20s shutter delay. I have many blurry photographs of the Moon which I took before figuring out the two-tripod solution. 

Metering

Adding three extenders reduced the usually very fast f/4 Tele-Tessar to a 'maximum' aperture of f/22. That's slow at the best of times, but through the Baader Astro Solar Safety Film it becomes very slow, indeed. The camera's meter only gave me 1/30th of a second so every photon counted. 

The Hasselblad 203FE has a large center-weighed metering spot which interestingly is almost exactly the same size as the Sun when seen through the Tele-Tessar and the three extenders. It was therefore easy to get an accurate meter reading. From some online sources I had read that the solar disk should be shot at faster shutter speeds at ISO 100 and an effective f/22, even up to 1/125 of a second, but I went with the in-camera meter for this photograph. The photographs I shot at such faster speeds are not useable.

Taking the shot

Focusing was tricky. One reason for this is that the Sun lacks distinguishing features. Compared with the Moon, for instance, which has readily visible craters which assist in finding accurate focus, the Sun is just a round disk. And on the day I shot this photo there weren't even any sunspots to help me.

Another reason for the focusing difficulties was the equipment I chose to use. The 350mm Tele-Tessar when coupled with the Hasselblad 203FE and its Acute Matte screen gives a very bright viewfinder image. The two 2x teleconverters can be stacked without making focus too difficult; it is the 1.4x PC-Mutar which is the main culprit. This accessory is not meant to be used as a teleconverter. Its 1.4x extension exists to enlarge the image circle of a lens no longer than 100mm in order to permit shifting the lens up to 16mm (but only 8mm with a 100mm lens) to correct converging verticals. In its neutral position, however, the PC-Mutar works just as any other extender and reduces the aperture by one stop (and, just to be clear, I used the PC-Mutar without the two cable releases normally necessary). Nevertheless, I find that the PC-Mutar softens the viewfinder image somewhat which makes it difficult to find accurate focus. A further complication was that the 350mm Tele-Tessar lacks a hard infinity stop on its focusing ring which added to the challenge. 

So, faced with a blank spotless solar disk, a darkish viewfinder image and a lack of hard infinity stop to assist me, I therefore had to use the edges of the Sun as the only feature on which I could focus. Looking at the shots on the roll, I can conclude that this works well even if it is necessary (and time consuming) to 'rack' focus back and forth to find the sharpest focus point.

Film choice, development and scanning

For this photograph I used Fuji Neopan Acros 100 which I exposed at box speed. Acros is a very fine-grained film which I chose because I like how it deals with contrasty (terrestrial) subjects. I figured that there is nothing more contrasty than the Sun so it ought to be OK. I think it was a good choice. 

I developed the film in Kodak HC-110 dilution E for about 7 minutes at 21 degrees Celsius. I know the Massive Development Chart says that 7 minutes is for 20 degrees Celsius, but I'm not that picky and it seems to have worked well enough.

With respect to agitation I followed my normal routine of 30 seconds initial (slow) agitation and then 2-3 turns every minute. I used Ilford's stop bath and fixer and washed as per normal filling the tank five times with 30 inversions each time. For the last rinse I used a few decilitres of distilled water to which I had added a few ml of Ilfotol to help get rid of drying marks. Then I hung the film to dry in the shower (but I did not run the hot water in advance; some say that the mist will get rid of dust particles in the air).

The Sun is not as large in the original frame as the above photograph shows; the final version is approximately a 40% crop of the frame. In order to get as large a solar disk as possible I scanned the negative with my Hasselblad Flextight X1 at maximum resolution, approximately 7000x7000px, before cropping. This let me get as large a solar disk as possible while retaining as much image information as possible in the image. 

Post-processing

With respect to post-processing, I must confess that I am a novice when it comes to solar photography. I therefore resorted to what I know and used the same workflow as I always do, meaning dust-spotting in Photoshop and then editing the image in Adobe Camera Raw.

As you can see at left, the unedited, straight out of the scanner version is considerably duller and less contrasty. A main goal in processing the image was to give the impression of a round object, rather than a flat disk, while avoiding to burn out the brighter centre portion of the disk.

This required first setting the black point low (the Blacks slider in Adobe Camera Raw), but not so low as to destroy the edges of the solar disk. The edges of the disk are slightly darker than the rest of the disk and easily get 'eaten up' by the surrounding darkness if the black point is set too low.  

I then adjusted the white point (the Whites slider) until I felt that the disk had sufficient luminosity. I did not manage to get the histogram's graph spread all the way to the right without clipping too much of the highlights. After this I adjusted the Shadows slider. I found that I could brighten the Highlights slider quite a bit without burning out the central portion of the disk. Then, I added a touch of Contrast and some Clarity. I found that these two sliders complemented each other well to help make the disk look slightly more three-dimensional. 

Finally, I sharpened the image and here the aim was to avoid the introduction of ugly artefacts. I am under no illusion that my camera and lens would have managed to capture the Sun's texture accurately, but I do find it interesting to look at the image at 100% because there is definitely some structure to its surface that is neither sharpening artefacts, nor grain.

Final thoughts

This was actually frame one of the first film I shot with the Baader Astro Solar filter. To be honest it was a slightly nerve-wracking experience to point the camera straight at the Sun protected only by a very thin and flimsy filter and I checked that it was properly secured with duct tape several times. I also shot the Sun using colour negative and transparency film but they do not work as well because the Baader filter essentially renders the Sun monochromatic. These films introduce unnecessary colour to the grain of the image. Black and white will therefore be my preferred film when using this filter. 

You may wonder about sunspots and why none is visible in the photo. Well, as (bad) luck would have it the Sun was spotless when I shot this image. To check how the Sun looks from day to day, Nasa maintains a useful page.

Whether or not one is a pipe smoker with ready access to tobacco tins I encourage anyone interested to try this type of photography. It is fascinating to view the Sun this way, and it plays tricks on one's mind in some way to see this massive object look like the bottom of an egg.